Cardiac abnormalities in myotonic dystrophy. Electrocardiographic and echocardiographic findings in 65 patients and 34 of their unaffected relatives. Relation with age and sex and relevance for gene detection.

Sixty-five patients with a definite diagnosis of myotonic dystrophy (MD) and 34 of their presumably unaffected relatives were examined cardiologically, including ECG in all and echocardiography in 61 and 32 persons respectively, in order to investigate the frequency of cardiac abnormalities, their clinical importance and their potential value as a preclinical marker in the diagnosis of MD. Atrioventricular conduction (AVC) abnormalities were found in 18/33 (54%) of affected males and in only 5/32 (16%) of affected females (P = 0.0025). Intraventricular (IVC) conduction abnormalities were encountered with similar frequency in both sexes: in 12/33 (36%) of affected males and 10/32 (31%) of affected females. Mitral valve prolapses (MVP) were seen more often in affected females: 9/31 (29%) of affected males vs 15/30 (50%) of affected females have MVP (P = 0.16). A previously undescribed finding was that of pericardial effusions in 5 affected and in 1 unaffected person. All affected males with MVP also had conduction abnormalities, but cardiac findings were not interrelated otherwise. None of the cardiac abnormalities mentioned were age-related. Only 8/65 (12%) of patients had cardiac symptoms, all of which were the result of conduction defects. As far as can be judged from a transversal study, the value of cardiac examination of this kind as a preclinical test for the diagnosis of MD is modest. It is argued that IVC-abnormalities, but not AVC-disturbances or MVP, in clinically unaffected relatives may indicate that they are preclinical heterozygotes. The significance of pericardial effusion for the diagnosis of MD awaits further evaluation.